Lisp insights from learning Logo

So I was just writing a simple recursive procedure in Logo. I wanted to go down a list, cons up a new list, and return the empty list when I get to the end.

My first pass, once I found out how to return something from a function (Logo procedures aren't expressions -- you have to explicitly return) had a line like this:

if (stacks = []) (output [])

Running the procedure gave me the helpful error message:
output didn't output to if in astep
[if (stacks = [] ) (output [] )]

Pardon?

When I remembered that Logo's "if" wants a list of instructions, it clicked with my new nugget of knowledge that literal lists are quoted in Logo. Then I understood what was going on: this "if" is neither a macro (like in Scheme, or most languages) nor lazily evaluated (like Haskell). It's a regular function, but one that expects quoted code to evaluate on demand at runtime. Rubyists and Smalltalkers: this is something like how an if block works for you, yes?

Here's an analogy into Python, for the non-Lispers out there:

def myIf(tf, truecode, falsecode):
  code = {True : truecode, False : falsecode}
  return eval(code[tf])

>>> myIf(0 == 1, "'it was ' + 'true'", "'it was not true'.upper()")
'IT WAS NOT TRUE'

>>> myIf(0 == 0, "'it was ' + 'true'", "'it was not true'.upper()")
'it was true'

Also, apparently Logo in general has dynamic scope -- which shouldn't surprise me, since lexical scope is relatively new in Lisp. And Berkeley Logo in particular has macros. Maybe my little compiler project is going to be harder than I expected. Honestly, I was imagining I'd be done if I could just parse it, do some simple transformations on the tree and spit JavaScript.

my code has a side effect: learning!

So I'm working through the exercises in Real World Haskell. Here's what I've got so far. As of this writing, I'm in the middle of chapter 4. RWH totally deserves all the buzz it's been getting; it's very approachable and well-written, and my Haskell is improving rapidly. The book is still free online, but I bought the printed copy, in large part because Bryan O'Sullivan gave such a great talk at OSCON.

My earlier Haskell project had stalled out due to my not being very good at the language yet. What I want to do is build a compiler for Logo that produces JavaScript, with the turtle graphics on a canvas tag. Logo is an acceptable Lisp! I'd love to see it get more use.

Interestingly, though:

• There's already a beautiful Logo implementation that runs in javascript: papert.
• Mark is working on something like papert, but for Processing -- he wants to put your Processing sketches, how you say, in the cloud.
  
• There are some really nice (and free!) introductory CS texts that feature Logo. Brian Harvey has a pretty serious three-volume set. And there's a version of How to Think Like a Computer Scientist done in Logo.
  

JES Prerelease!

I packaged up the next release of JES, our "Media Computation" environment for helping beginning programmers today. Honestly, if I was teaching kids about programming, I'd probably use this. It's a lot faster than the previous versions, it has a better layout and clever integrated help, it has LOGO turtles!, and like always -- it's really good for doing funky stuff to pictures. (gallery 1, gallery 2).

Fresh code! Here!

Any feedback would be greatly appreciated!
(slides for cs1315, the course where we make use of JES can be found here, in case you want to play around with JES but don't know what it's good for yet!)

Beautiful educational software :)

So many of you are probably aware that my job (ie: research assistantship, ie: how I'm getting gradschool paid for) is to work on JES, the Jython Environment for Students -- it's the little IDE that we use at Georgia Tech to teach introductory CS classes to non-majors and for summer camps as part of our "media computation" effort. A number of other schools use our stuff too, which makes me pretty happy. We're releasing a new version soon, and it's going to rock hard and be faster and include LOGO-style turtles! I'll put up links when it's out.

But speaking of LOGO-style turtles and media computation:
- The KDE Project has KTurtle out now, which looks pretty cool. It's part of their bigger KDE Edutainment effort.
- TuxPaint is also pretty cool! My friend (and noted cartoonist) Brett finds it pretty amusing. It reminds me of KidPix, which you might remember from your childhood if you're about as old as me -- and that's still out there, apparently?
- Tux Paint comes to us from New Breed Software, which has a bunch of other cool educational products.
- And if you only click one link on this post: Pictures Kids Made With TuxPaint

And, for completeness:
- Alice is a programmable 3D environment up outta CMU that rocks harder than I can describe in a quick blog post. As they put it on their site, "Alice will make programming a means to an exciting end." That exciting end is really easy 3D storytelling.

Red pandas and rhinoceri and turtles? ...

Why is there not a client-side javascript version of LOGO?

How cool would that be? Turtles in your browser? ... Small children having access to Papertian goodness wherever the Internets are tubin'?